Radiation detector having a unitary reflector part composed of plastic containing an optically reflective filler

ABSTRACT

A radiation detector has a photodiode arrangement, a number of scintillators, and a reflector part having a number of compartments corresponding to the number of scintillators, which receive the scintillators in such a way that the scintillators are surrounded by walls of the compartments with the exception of their side respectively facing the photodiode arrangement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiation detector of the type havinga number of scintillators which emit light when radiation to be detectedis incident thereon, the light being detected by photodiodes of aphotodiode arrangement.

2. Description of the Prior Art

Radiation detectors of the above type are used in computed tomographysystems, for example. If X-ray quanta are incident on the scintillators,which are composed of a suitable luminescent material, for exampleluminescent ceramic, the X-ray quanta are converted into light quanta.The light quanta are converted by the photodiodes into an electriccurrent corresponding to the intensity of the light, and this current isamplified by an electronic unit and converted into digital data whichare processed to form X-ray images by means of a computer associatedwith the computer tomography system.

In order to obtain a maximum light yield on the photodiode, thescintillators, composed of an optically transparent or translucentluminescent material, are surrounded by an optically reflective materialon all sides except on their side facing the photodiode arrangement.

The scintillators are usually provided with a scattered radiationcollimator whose collimator plates are oriented to the focus of an X-raysource interacting with the radiation detector, so that essentially onlyX-ray radiation emerging from the X-ray source can pass to thescintillators, while the scattered radiation produced when carrying outan examination in the object under examination is for the most part keptaway from the scintillators.

In a known radiation detector of modular construction for a computedtomography system, each module has a photodiode arrangement with anumber of photodiodes which are each assigned a scintillator. In thiscase, the scintillators are not separate elements since this would makeit more difficult, if not impossible, to effect the exact positioning ofthe scintillators relative to the photodiodes.

A scintillator part is used whose length and width have a certainoversize relative to the length and width of the photodiode arrangement.

This scintillator part is encapsulated at its periphery and top sidewith a reflector coating, e.g. epoxy resin filled with titanium oxide,which serves as an optical reflector. In this case, a defined layerthickness is ensured at the periphery by special casting molds. At thetop side, a defined layer thickness is ensured by mechanical processingin a special apparatus.

Afterward, the scintillator part is positioned on the photodiodearrangement by means of a special apparatus and adhesively bonded tosaid arrangement, in which case the apparatus can be removed again onlyafter the adhesive bonding has cured.

The elements thus produced are laterally trimmed by specialhigh-precision abrasive cutting machines and the scintillator element isslotted in such a way that each photodiode of the photodiode arrangementis allocated to a scintillator. In this case, particular attention mustbe paid to the slot depth in order to avoid damage to the photodiodes.So-called septa, for example aluminum foils coated on both sides, areadhesively bonded into the slots bounding the scintillators. The trimmedareas of the scintillator part are likewise bonded to septa.

Another manufacturing concept is based on adhesively bonding in eachcase a scintillator and a photodiode to one another and assembling alarge number of such detector elements to form a radiation detector. Itis possible in this case as well to combine a number of detectorelements to form detector modules.

If it is intended to use a scattered radiation collimator, in bothmanufacturing concepts it is complicated and difficult to position thescattered radiation collimator before the adhesive bonding to theradiation detector or detector modules relative to the latter in therequired manner. Therefore, complicated apparatuses are used in whichthe scattered radiation collimator and the radiation detector or thedetector module must remain until the adhesive bonding has cured.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a radiation detector ofthe type mentioned in the introduction which can be produced in a simpleand uncomplicated manner.

The above object is achieved in accordance with the principles of thepresent invention in a radiation detector having a photodiodearrangement with a number of scintillators and an optically reflectivepart having a number of compartments therein equal to the number ofscintillators, with the scintillators being respectively received in thecompartments, so that each scintillator is surrounded by the walls ofthe compartment except for a side of the scintillator that faces towardthe photodiode arrangement.

In the case of the invention, thus, the reflector part not only renderssuperfluous the septa required in the prior art as well as the coatingwith reflector coating, but additionally ensures that the scintillatorsassume defined positions relative to one another and relative to thephotodiodes of the photodiode arrangement.

Consequently, the processing of the scintillators is restricted totailoring them to the dimensions corresponding to the compartments inorder that they can be inserted into the compartments of the reflectorpart, where they are fixed by adhesive bonding in accordance with onevariant of the invention. As already mentioned, then, potting withreflector coating is not necessary, with the result that the expensivecasting molds required for this can be obviated. Moreover, there is noneed for expensive special machines for processing the scintillators.

Furthermore, the slotting operations required in the prior art and theassociated risk of damaging photodiodes of the photodiode arrangementare obviated. Finally, as mentioned, septa are not required, whichrenders superfluous the production and handling of these sensitiveadditional parts.

Thus the radiation detector according to the invention can be producedin a significantly simpler, less complicated and thus morecost-effective manner than in the prior art.

In a preferred embodiment of the invention, the reflector part is ofone-part design, i.e., unitary or seamless, for example as aninjection-molded or die-cast part, which is preferably produced fromplastic, in particular a plastic containing an optically reflectivefiller. By virtue of such a design of the reflector part, the latter andthus the radiation detector overall can be produced in a simpler andmore cost-effective manner.

In a further preferred embodiment of the invention the reflector partand the photodiode arrangement have centering means which interact withone another and which, in the case of the arrangement of the reflectorpart in front of the photodiode arrangement, ensure that thescintillators are arranged opposite the respectively associatedphotodiode. This measure further simplifies the production of theradiation detector according to the invention, since no complicatedmeasures or apparatuses are required for ensuring the required definedposition of reflector part and photodiode arrangement relative to oneanother.

In a further embodiment of the invention, the radiation detector has ascattered radiation collimator with collimator plates which is arrangedin front of the reflector part. The reflector part and the scatteredradiation collimator have centering means which interact with oneanother and which, in the case of the arrangement of the scatteredradiation collimator in front of the reflector part, ensure that thecollimator plates of the scattered radiation collimator are aligned withwalls of the reflector part which surrounds the compartments. Thismeasure ensures, in a simple manner, in particular without complicatedapparatuses, that the scattered radiation collimator and the reflectorpart are positioned correctly relative to one another.

In another embodiment of the invention the radiation detector iscomposed of a number of modules, each of which has a reflector part withscintillators and a photodiode arrangement, in which case each modulecan be allocated to a scattered radiation collimator.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective, exploded view of a radiation detectorconstructed in accordance with the principles of the present invention

FIG. 2 is a perspective view of the reflector part of the radiationdetector of FIG. 1.

FIG. 3 is a sectional view taken along line III—III of FIG. 2.

FIG. 4 illustrates a modularly constructed radiation detector inaccordance with the invention.

FIGS. 5 and 6 are sectional views illustrating an embodiment for themanufacture of the radiation detector according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As can be seen in FIG. 1, the exemplary embodiment of a radiationdetector according to the invention which is illustrated in FIGS. 1 to 3has, as essential elements, a photodiode arrangement 1 with photodiodes3 fitted on a substrate 2, a reflector part 5 containing scintillators 4and a scattered radiation collimator 6 with collimator plates 8 fittedbetween two side parts 7.

As can be seen from FIG. 2 in conjunction with FIG. 3, the reflectorpart 5 has a base plate 9, on which a frame-shaped boundary wall 10 isfitted.

The space surrounded by the boundary wall 10 is subdivided into a numberof compartments, one of which is provided with the reference symbol 12,by partitions 11 running parallel to one another and parallel to twomutually opposite sections of the boundary wall 10.

The compartments 12 each receive a rod-shaped scintillator 4 which isadhesively bonded into the respective compartment 12.

The dimensions of the scintillators 4 are coordinated with thecompartments in such a way that said scintillators completely fill saidcompartments.

In the case of FIGS. 2 and 3, only some of the compartments 12 containscintillators 4, in order to be able to illustrate the configuration ofthe compartments 12. It is understood, however, that all thecompartments 12 of the reflector part 5 contain scintillators 4 in theassembled state.

Thus the individual scintillators 4, except at their side facing thephotodiode arrangement 1, are surrounded by walls of the reflector part5, whether by the base plate 9, or by the boundary wall 10 or by thepartitions 11.

Since the reflector part 5, which is designed as an injection-molded ordie-cast part, is formed from an optically reflective material, fromepoxy resin treated with titanium oxide in the case of the exemplaryembodiment described, the reflector part 5 takes over the functionswhich are performed by the septa and the covering with reflector coatingin the case of the prior art.

The reflector part 5 containing the scintillators 4 and the photodiodearrangement 1 are joined together to form a unit, which can be done byadhesive bonding, for example to assure that the joined componentsassume a defined position relative to one another in which the freesides of the scintillators 4, which face the photodiode arrangement 1,are arranged opposite the photodiode of the photodiode arrangement 1which is allocated to the respective scintillator 4, so that the activeareas of the photodiodes are congruent with the free sides of thescintillators 4, the photodiode arrangement and the reflector part 5 areprovided with centering means which interact with one another.

In the exemplary embodiment, these centering means are pins 13 which arefitted at the edge of the reflector part 5 and engage in correspondingopenings 14 of the photodiode arrangement 1.

In order also to ensure a correct position of the scattered radiationcollimator 6 relative to the reflector part 5 with the scintillators,the reflector part 5 and the scattered radiation collimator 6 are alsoprovided with centering means which interact with one another, pins 15fitted on the scattered radiation collimator 6 being involved whichinteract with openings 16 provided on the reflector part 5 and ensurethat the collimator plates 8 of the scattered radiation collimator 6 arealigned with the partitions 11 of the reflector part 5.

As can be seen from FIG. 4, it is possible for a radiation detectoraccording to the invention to be composed of a number of modules, eachof which has a reflector part with scintillators, a photodiodearrangement and, if required, a scattered radiation collimator. Such asubdivision into modules affords the advantage, for example, that theindividual modules are easy to handle.

In the exemplary embodiments the rectangular photodiodes 3 aresubdivided into, for example, square photodiode segments 17. Such asubdivision may be expedient, but is not absolutely necessary.

The construction of the centering means described in connection with theexemplary embodiments is only an example. The centering means can beembodied differently.

As an alternative to the procedure provided in the exemplary embodimentin accordance with FIGS. 1 to 3, namely of adhesively bonding separaterod-shaped scintillators 4 into the compartments 12 of the reflectorpart 5, it also is within the scope of the invention, in accordance withFIGS. 5 and 6, to first produce a scintillator blank 18 from a plate ofscintillator material by the plate being structured by slots so that thescintillator blank 18 has a relatively thin base plate 19 withrod-shaped scintillators 4 situated thereon and configured to be anegative of the reflector part 5. This scintillator blank 18 is insertedinto the reflector part 5 in such a way that a scintillator 4 issituated in each of the compartments 12, and is adhesively bonded to thereflector part 5 in such a way that there is an adhesive bond betweeneach of the scintillators 4 situated on the base plate 19 and therespectively corresponding compartment 12 of the reflector part 5. Afteradhesive bonding has been effected, the base plate 19 is removed bymaterial-removing machining, e.g. grinding, so that all that remains ofthe scintillator blank 18 are the scintillators 4 adhesively bonded tothe compartments 12 of the reflector part 5.

The radiation detector according to the invention in accordance with theexemplary embodiments is provided for computed tomography. However,radiation detectors according to the invention can be used in generalX-ray technology and also for the detection of ionizing radiation whosewavelength range lies outside the length range characteristic of X-rayradiation.

Although modifications and changes may be suggested by those skilled inthe art, it is the invention of the inventors to embody within thepatent warranted heron all changes and modifications as reasonably andproperly come within the scope of their contribution to the art.

1. A radiation detector comprising: a plurality of scintillators which emit light when penetrating radiation is incident thereon; a photodiode arrangement comprising a plurality of photodiodes disposed to detect light emitted by said plurality of scintillators, each of said scintillators in said plurality of scintillators having a side facing said photodiode arrangement; and a reflector part, formed separately as a one-piece unit composed of plastic, said plastic containing an optimally reflective filler, said reflector part reflecting said light and having a plurality of compartments equal to said plurality of scintillators, said scintillators in said plurality of said scintillators being respectively disposed in said compartments and, in said compartments, being surrounded by walls of said compartments on all sides except said side facing said photodiode arrangement.
 2. A radiation detector as claimed in claim 1 wherein said reflector part and said compartments of said reflector part are disposed relative to said photodiode arrangement so that one scintillator in said plurality of scintillators is disposed opposite one photodiode of said photodiode arrangement.
 3. A radiation detector as claimed in claim 1 comprising adhesive bonding fixing the respective scintillators in said compartments.
 4. A radiation detector as claimed in claim 1 wherein said reflector part is seamless.
 5. A radiation detector as claimed in claim 1 wherein said reflector part is an injection-molded part.
 6. A radiation detector as claimed in claim 1 wherein said reflector part is a die-cast part.
 7. A radiation detector as claimed in claim 1 further comprising centering elements disposed on said reflector part and said photodiode arrangement which interact with each other to maintain said scintillators in said plurality of scintillators at respective positions relative to said photodiodes in said photodiode arrangement.
 8. A radiation detector as claimed in claim 1 further comprising a scattered radiation collimator having collimator plates disposed in front of said reflector part.
 9. A radiation detector as claimed in claim 8 wherein said reflector part and said scattered radiation collimator have respective centering elements which interact with each other to maintain said collimator plates of said scattered radiation collimator aligned with said walls of said reflector part which form said compartments in which the respective scintillators are disposed.
 10. A radiation detector as claimed in claim 1 wherein said plurality of scintillators, said photodiode arrangement and said reflector part comprise a first module, and wherein said radiation detector comprises a plurality of additional modules, identical to said first module, disposed adjacent to each other.
 11. A radiation detector as claimed in claim 10 further comprising a plurality of scattered radiation collimators respectively disposed in front of each of said first module and said plurality of additional modules. 